Photoelectron diffraction in the x-ray and ultraviolet regime: Sn-phthalocyanine on Ag(111)

Abstract

The bonding geometry of tin-phthalocyanine (SnPc) on Ag(111) has been studied using x-ray and ultraviolet photoelectron diffraction (XPD and UPD, respectively). Experimental diffraction patterns were compared to single-scattering-cluster calculations. XPD data could be well reproduced by the simulations and allowed for the determination of several structural parameters. At a coverage of 0.9 ML all molecules are in a "tin-down" configuration and the non-planar shuttlecockshaped SnPc molecule undergoes flattening upon absorption on Ag(111). UPD data from the second highest occupied molecular orbital (HOMO-1) turn out to be highly sensitive to minor structural changes, including also the vertical distance between tin atoms of the SnPc and the surface layer of the substrate, which is found to be 2.3Å. We thus demonstrate how UPD can complement the well-established XPD method and discuss remaining challenges in the theoretical description of photoelectron diffraction from molecular orbitals at low energies. The UPD method is particularly attractive in view of the increasing availability of ultrashort pulsed laser sources in the XUV regime, which could enable pump-probe experiments with high structural sensitivity.

Surface chemistry of porphyrins and phthalocyanines

“…SnPc on Ag(1 1 1) was also studied by X-ray and UV photoelectron diffraction. At 0.9 ML, an all-SnPc↓ phase was observed with Sn-Ag and C-Ag distances of 2.3 and 3.09 Å, respectively [334]. For a complex with a planar gas-phase structure such as CuPc or CoPc, the distance between metal center and substrate is typically larger than in the case of a shuttlecock-shaped complex in the metal-down orientation [199,231].…”

“…Most of the related studies were performed with the normal-incidence X-ray standing wave (NIXSW) technique [329], which was applied to SnPc/Ag(1 1 1) [196][197][198][199], CuPc on Cu(1 1 1) [233], Ag(1 1 1) [197,231,330] [332], 2HPc/Ag(1 1 1) [333], CoPc/Ag (1 1 1) [199], and PbPc/Ag(1 1 1) [199]. In addition, photoelectron diffraction (PED) has been used for the structural analysis of SnPc/Ag(1 1 1) [334] and (O)VPc/Au(1 1 1) [335].…”

Sensitivity of photoelectron diffraction to conformational changes of adsorbed molecules: Tetra-tert-butyl-azobenzene/Au(111)

“…The coherent sum is then evaluated at the position of detection in the far field. The computations are done by using a cluster model of the substrate, which allows adsorbed molecules to be included in a straightforward fashion 14 . The atomic positions of the trans and cis isomers of TBA adsorbed on Au(111) were taken from the DFT calculation of McNellis et al 11 The two clusters consist of a single TBA molecule ( trans and cis ) on a gold (111) substrate.…”

Access to phases of coherent phonon excitations by femtosecond ultraviolet photoelectron diffraction

“…The angular intensity distribution of the photoelectrons is furthermore modulated by interference effects of scattered photoelectron waves and, thereby, provides direct information about the atomic structure of the surface. This effect is called photoelectron diffraction and can be seen in angular distributions excited by x rays (XPD) [17,18] or ultraviolet light (UPD) [19][20][21]. We demonstrate that the dynamics of the full process can be investigated by tr-ARPES and photoelectron diffraction using light from a high-harmonic laboratory source.…”